precision of application, not only with chemi- 
cals but with other methods, suchas biological 
control, Insect viruses have been tested as a 
means of controlling cabbage loopers, corn 
earworms, and the tent caterpillar, Such ap- 
plications may need to be extremely precise, 
since, for example, a man could hold on his 
fingernail enough cabbage looper virus con- 
centrate to treat 5 acres, 
Aerial Application 
Research today indicates that spray dis- 
charged along the lateral axis of an aircraft will 
follow the airflow set in motion by its passage 
through the air until the accompanying forces 
will no longer support the spray droplet, The 
airplane develops three principal airstreams, 
which affect spray distribution: The two wing- 
tip vortices and the propeller vortex, These 
vortices, plus the effects of gravity and 
atmospheric turbulence, determine the path of 
the pesticide discharge and the resultant de- 
posit pattern, Although it is obviously impos- 
sible to eliminate propeller and wing-tip 
vortices, at least with today's airplanes, re- 
search is underway by public and private 
agencies to develop a new type of airplane 
configuration that will permit much better con- 
trol of aerial pesticide application and of pesti- 
cide drift, The airplane is now virtually a 
standard agriculturalimplement, and improve- 
ments will continue to be made for this ac- 
tivity. 
We are only beginning to understand the air- 
flow effects surrounding the helicopter, but re- 
search is underway to determine under what 
conditions it will be more or less Suitable 
than a conventional aircraft in pesticide ap- 
plication, The Agricultural Engineering Re- 
search Division of the U.S, Department of 
Agriculture now has available one helicopter, 
from which are being developed experimental 
data that we hope will be of considerable use- 
fulness, 
Granular Materials 
Seldom has a farming practice had such 
rapid acceptance as the use of granular insec- 
ticides and herbicides, Many farmers are now 
practicing chemical weed and insect control 
210 
utilizing granular materials and equipment, 
The desirable characteristics of application 
vary with the crop, the insect, and the chem- 
ical used, 
Ideally, the discharge from a granular ap- 
plicator should be proportional to the ground 
speed, but, because of the nature of the ma- 
terials, no completely satisfactory type of 
metering device has yet been available (16), 
As more selective and more toxic chemicals 
appear, greater accuracy will be needed, For 
example, for corn borer control, spreading 
devices that will apply granules in 14- to 
20-inch bands directly over the corn plants 
are recommended, For soil insect control, 
granules are dropped directly out of the dis- 
charge tubes for both band and overall ap- 
plications, As with other equipment, the speci- 
fications for control need to be established so 
that equipment can be developed to fill the 
need, 
Granular insecticides can be applied by hand 
as, e.g., has been done in orchardtests, where 
the soil under trees was treated with aldrin 
granules (28), However, the economical ap- 
plication of granular insecticides over large 
acreages naturally requires the use of power- 
driven spreaders, More specific machines and 
attachments need to be developed as, e.g., in 
the case of preemergence herbicides or soil 
insecticides, where application of less than 90 
percent of the recommended rate can result 
in ineffective control and application rates 
higher than recommended can be costly or 
may injure the crop (4), 
Particulate Spray 
An interesting new approach to the reduc- 
tion of pesticide drift pertains to the develop- 
ment of controlled drop sizes, according to the 
particulate spray concept (7), In this process, 
a water solution is imbibed by particles of a 
polymer known as a "particulating agent," 
whose particles subsequently swell to many 
times their dry volume, yet they do not dis- 
solve, If the swelling capacity of the particulat- 
ing agent added to the solution is just equal 
to the solution volume, essentially allthe spray 
solution will be immobilized in the swollen 
polymer particles, The minimum size of 
swollen particles is governed by the dry size 
